Digital cameras are known in the art as devices capable of taking still pictures or video by capturing images on an electronic image sensor, and digitally storing the captured image or video on a digital memory, usually after digital compression and embedding in known file formats, such as e.g. JPEG for still pictures, and e.g. AVI or MOV for movies. A digital camera can be a stand-alone dedicated device, or may be embedded in another device, such as e.g. a mobile phone, a laptop computer, etc.
Digital cameras have evolved substantially over the years, not only in image resolution and storage capacity, but also in features for facilitating the capturing of high quality pictures under highly varying circumstances, e.g. light/dark scenes, far/near objects, still/moving objects, etc.
An important aspect is that of light/dark scenes, which is related to the amount of incoming light. The term “over-exposure” is used to indicate that too much light enters the image sensor, such that some or most or all of the sensor elements are saturated. The term “under-exposure” is used when the amount of incoming light is insufficient for having a good contrast ratio or dynamic range. In order to avoid over-exposed (“too bright”) or under-exposed (“too dark”) images, several settings, such as e.g. “aperture” (or opening) and shutter time (or exposure time), need to be correctly set, for determining the amount of incoming light. “Aperture” is the diameter of an opening with an adjustable diameter centred on the optical axis in order to adjust the light quantity and the extent of blur.
While in early cameras one or more of these settings needed to be set manually, many modern cameras are provided with automatic light metering, and/or auto-focus, and/or automatic determination of the exposure time.
U.S. Pat. No. 8,009,223 describes a digital camera having an image sensor with both “image pixels” and “non-image pixels” (also referred to as “focus-detection pixels”). The non-image pixels are different from the surrounding image pixels, and are designed for providing information for automatically focusing the lens. The focus-detection pixels do not contribute to the normal shooting of an image, i.e. they do not provide actual image data. An algorithm is described for determining a defocus amount, and for adjusting the focus point of the lens accordingly. An algorithm is also provided for determining pixel data at the location of the focus detection pixels, through interpolation of imaging pixels present near the focus detection pixels. However, this document does not describe how the light metering is done, nor how the exposure time is determined.
US20120013762 describes a solid state camera adapted for automatically determining a final exposure setting (including e.g. gain, integration time and aperture), by assuming initial exposure settings, and then repeatedly capturing a full image using the previously determined exposure settings, and adjusting the exposure setting based on histogram information of the full image data thus taken, until optimal exposure settings are found, and then taking the final image using the final exposure settings. Besides of being complicated, this method suffers from a long latency (time between pressing “the button” and the time when the image is actually captured).